By some calculations, the rock, an asteroid or a comet that crossed Earth's path, should have hit the ground at 72,000 kilometres per hour, for it left a huge crater 1.2 kilometres across and 150 metres deep.

If so, the high-velocity collision should have released so much heat that the iron-rich impacting rock itself, or at least part of it, should have melted in a flash. But no substantial signs of melted mineral have ever been found there.

The reason, according to the new study: the rock was merely the largest chunk from a space bruiser that probably measured 42 metres across.

After entering Earth's atmosphere, the giant broke apart at an altitude of around 14 kilometres as it encountered a steadily denser atmosphere, whose pressure both cushioned the descent and caused the rock to fracture.

The fragments then descended in a pancake-shaped cluster, with atmospheric drag acting as a brake.

The piece that created Meteor Crater was probably around 20 metres across and hit the ground at 43,000 kilometres per hour, releasing the equivalent force of 2.5 megatons of TNT, or at least 150 times the "Little Boy" atomic bomb dropped on Hiroshima in 1945, the study suggests.